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| United States Patent |
5,566,367
|
|
Mitsutake
, et al.
|
October 15, 1996
|
Plate-like polarizing element, a polarizing conversion unit provided
with the element, and a projector provided with the unit
Abstract
This specification discloses a plate-like polarizing element for converting
light into polarized light having a plurality of units arranged along a
common plane across the light, each of the units being provided with
dividing means for dividing the light into reflected light and transmitted
light whose planes of polarization are orthogonal to each other, varying
means for varying the polarized state of at least one of the reflected
light and the transmitted light to thereby make the planes of polarization
of the two lights coincident with each other, and reflecting means for
reflecting one of the reflected light and the transmitted light and
directing it substantially in the same direction as the direction of
travel of the other. The specification also discloses a polarizing
conversion unit provided with such plate-like polarizing element, and a
projector provided with such unit.
| Inventors:
|
Mitsutake; Hideaki (Tokyo, JP);
Mochizuki; Noritaka (Yokohama, JP);
Kawasaki; Shigeru (Atsugi, JP);
Kimura; Kazumi (Atsugi, JP);
Shingaki; Junko (Atsugi, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
163564 |
| Filed:
|
December 8, 1993 |
Foreign Application Priority Data
| Current U.S. Class: |
359/497; 359/485; 359/495 |
| Intern'l Class: |
G02B 005/30; G02B 027/28 |
| Field of Search: |
359/487,494,495,497,498,499,48,49,63
|
References Cited
U.S. Patent Documents
| 2449287 | Sep., 1948 | Flood | 359/495.
|
| 2748659 | Jun., 1956 | Geffcken et al. | 359/495.
|
| 2810324 | Oct., 1957 | Marks.
| |
| 2868076 | Jan., 1959 | Geffcken et al. | 359/495.
|
| 3876285 | Apr., 1975 | Schwarzmuller | 359/495.
|
| 4560999 | Dec., 1985 | Tokuhara.
| |
| 4827334 | May., 1989 | Johnson et al. | 359/495.
|
| 4864390 | Sep., 1989 | McKechnie et al.
| |
| 4989076 | Jan., 1991 | Owada et al.
| |
| 5073830 | Dec., 1991 | Loucks | 359/495.
|
| 5124841 | Jun., 1992 | Oishi | 359/495.
|
| Foreign Patent Documents |
| 935663 | Jan., 1956 | DE.
| |
| 61-90584 | May., 1986 | JP.
| |
| 63-182987 | Jul., 1988 | JP.
| |
Other References
European Patent Office: Patent Abstracts of Japan, Publication #:
JP62059919, Date: 16 Mar. 1987.
|
Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Schuberg; Darren E.
Attorney, Agent or Firm: Morgan & Finnegan, L.L.P.
Parent Case Text
This is a continuation of application Ser. No. 07/865,312, filed on Apr. 8,
1992, now abandoned.
Claims
What is claimed is:
1. A projector comprising:
illuminating means for emitting light;
a plate-like polarizing element for converting the light from said
illuminating means into polarized light, said plate-like polarizing
element comprising a plurality of units arranged along a common plane
across the light from said illuminating means;
each of said units comprising:
dividing means for dividing the light from said illuminating means into
reflected light and transmitted light whose planes of polarization are
orthogonal to each other, wherein said dividing means comprises a pair of
polarization separation acting surfaces obliquely provided in the optical
path from said illuminating means so as to face each other and disposed
with one end of one of them being in contact with one end of the other;
varying means for varying the plane of polarization of at least one of said
reflected light and said transmitted light to thereby make the planes of
polarization of said two lights coincident with each other, wherein said
varying means comprises a half wavelength plate installed between said
pair of polarization separation acting surfaces;
reflecting means for reflecting one of said reflected light and said
transmitted light and directing it substantially in the same direction as
the direction of travel of the other, wherein said reflecting means
comprises a pair of reflecting surfaces disposed so as to interpose said
pair of polarization separation acting surfaces therebetween and
reflecting said reflected light from one of said pair of polarization
separation acting surfaces through said half wavelength plate and the
other polarization separation acting surface;
converting means provided on the light incidence side of said plate-like
polarizing element for dividing said light into a plurality of partial
lights, condensing each of said partial lights and converting it into
light of a lattice-like pattern, each of said partial lights of a
lattice-like pattern corresponding to each of said units;
an image generator for modulating said polarized light in conformity with a
video signal to thereby generate an image; and
a projecting optical system for projecting said image.
2. A projector according to claim 1, wherein said half wavelength plate is
disposed intermediately of the optical path between said pair of
polarization separation acting surfaces.
3. A projector according to claim 1 wherein said plate-like polarizing
element is disposed so as to be substantially orthogonal to the optical
axis of said light of a lattice-like pattern emerging from said converting
means, transmits said light of a lattice-like pattern therethrough and
converts it into substantially dense polarized light.
4. A projector according to claim 3 wherein said converting means is a
both-surface fly-eye lens.
5. A projector according to claim 3 wherein said converting means is a
both-surface lenticular lens.
6. An image forming apparatus comprising:
means for providing light;
a plate-like polarizing element for converting the light from said
providing means into polarized light, said plate-light polarizing element
comprising a plurality of units arranged along a plane across the light
from said providing means;
each of said units comprising:
dividing means for dividing the light from said providing means into
reflected light and transmitted light whose planes of polarization are
orthogonal to each other, wherein said dividing means comprises a pair of
polarization separation surfaces obliquely provided in the optical path
from providing means so as to face each other and disposed with one end of
one of them being contact with one end of the other;
varying means for varying the plane of polarization of at least one of said
reflected light and said transmitted light to thereby make the planes of
polarization of said two lights coincident with each other, wherein said
varying means comprises a half wavelength plate disposed between said pair
of polarization separation surfaces;
reflecting means for reflecting one of said reflected light and said
transmitted light and directing it substantially in the same direction as
the direction of travel of the other, wherein said reflecting means
comprises a pair of reflecting surfaces disposed so as to interpose said
pair of polarization separation surfaces therebetween and reflecting said
reflected light from one of said pair of polarization separation surfaces
through said half wavelength plate and the other polarization separation
surface; and
an image generator for modulating said polarized light to thereby generate
an image;
said image from apparatus further comprising:
an optical system for projecting said image; and
changing means disposed at a light incident side of said plate-like
polarizing element,
wherein said changing means divide the light from said providing means into
a plurality of partial light beams to converge each of said plurality of
partial light beams to make the converged each thereof incident on a
corresponding unit of said plurality of units.
7. An apparatus according to claim 6,
wherein said each of said plurality of partial light beams becomes a
parallel light beam to be incident on said corresponding unit.
8. An image forming apparatus comprising;
means for providing light;
a plate-like polarizing element for converting the light from said
providing means into polarized light, said plate-like polarizing element
comprising a plurality of units arranged along a plane across the light
from said providing means;
each of said units comprising:
dividing means for dividing the light from said providing means into
reflected light and transmitted light whose planes of polarization are
orthogonal to each other, wherein said dividing means comprises a pair of
polarization separation surfaces obliquely provided in the optical path
from said providing means so as to face each other and disposed with one
end of one of them being contact with one end of the other;
varying means for varying the plane of polarization of at least one of said
reflected light and said transmitted light to thereby make the planes of
polarization of said two lights coincident with each other, wherein said
varying means comprises a half wavelength plate disposed between said pair
of polarization separation surfaces;
reflecting means for reflecting one of said reflected light and said
transmitted light and directing it substantially in the same direction as
the direction of travel of the other, wherein said reflecting means
comprises a pair of reflecting surfaces disposed so as to interpose said
pair of polarization separation surfaces therebetween and reflecting said
reflected light from one of said pair of polarization separation surfaces
through said half wavelength plate and the other polarization separation
surface; and
an image generator for modulating said polarized light to thereby generate
an image;
said image forming apparatus further comprising:
changing means disposed at a light incident side of said plate-like
polarizing element,
wherein said changing means divide the light from said providing means into
a plurality of partial light beams to converge each of said plurality of
partial light beams to make the converged each thereof incident on a
corresponding unit of said plurality of units.
9. An apparatus according to claim 8,
wherein said each of said plurality of partial light beams becomes a
parallel light beam to be incident on said corresponding unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plate-like polarizing element, a polarizing
conversion unit provided with the element, and a projector provided with
the unit.
2. Related Background Art
As an apparatus for converting non-polarized light having a random plane of
polarization into polarized light, an apparatus described in Japanese
Laid-Open Patent Application No. 61-90584 is shown in FIG. 1 of the
accompanying drawings.
In this projector, non-polarized parallel light emerging from a condenser
lens 104 enters a polarizing beam splitter 111, and P-polarized light
L.sub.P is intactly transmitted through the acting surface (evaporated
film formed on an inclined surface on which two rectangular prisms are
adhesively secured to each other) 111a of the polarizing beam splitter
111, while S-polarized light L.sub.S is upwardly reflected at a right
angle and enters a total reflection prism 112. The S-polarized light
L.sub.S is rightwardly reflected at a right angle by the total reflection
prism 112, whereby it emerges from the total reflection prism 112 in the
same direction as the P-polarized light L.sub.P transmitted through the
polarizing beam splitter 111. The S-polarized light L.sub.S refers to
rectilinearly polarized light having a plane of polarization parallel to
the acting surface 111a of the polarizing beam splitter 111, and the
P-polarized light L.sub.P refers to rectilinearly polarized light having a
plane of polarization orthogonal to the S-polarized light L.sub.S. A half
wavelength plate 113 is disposed on the emergence side of the total
reflection prism 112, and the S-polarized light L.sub.S which has emerged
from the total reflection prism 112 is transmitted through the half
wavelength plate 113, whereby the plane of polarization thereof is rotated
by 90.degree. and the S-polarized light L.sub.S is converted into
P-polarized light L.sub.P *. Also, wedge type lenses 114 and 115 for
changing optical path are disposed on the emergence sides of the
polarizing beam splitter 111 and the half wavelength plate 113,
respectively, and the P-polarized light L.sub.P transmitted through the
polarizing beam splitter 111 and the P-polarized light L.sub.P * converted
by the half wavelength plate 113 have their optical paths changed, and
intersect each other at a point P.sub.0 on the incidence side surface of a
liquid crystal light valve 117 and become combined light.
Accordingly, in this projector, the liquid crystal light valve 117 can be
illuminated by both of the S-polarized light L.sub.S and the P-polarized
light L.sub.P separated by the polarizing beam splitter 111. However, the
above-described projector of Japanese Laid-Open Patent Application No.
61-90584 requires the large polarizing beam splitter 111 and total
reflection prism 112, and this leads to the disadvantage that the entire
apparatus becomes bulky and heavy.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a plate-like
polarizing element which can cause non-polarized light emitted from a
light source to enter an image generator without any loss and can
contribute to the compactness of a projector, a polarizing conversion unit
provided with the element, and a projector provided with the unit.
The plate-like polarizing element of the present invention comprises a
plurality of units each having a dividing portion for dividing incident
light into reflected light and transmitted light whose planes of
polarization are orthogonal to each other, a reflecting portion for
reflecting one of said reflected light and said transmitted light and
directing it substantially in the same direction as the direction of
travel of the other, and a modulating portion for varying the plane of
polarization of at least one of said reflected light and said transmitted
light to thereby make the planes of polarization of the two coincident
with each other, said units being juxtaposed.
The polarizing conversion unit of the present invention has the plate-like
polarizing element of the present invention, and conversion means provided
on the incidence side of the plate-like polarizing element for converting
non-polarized light into non-polarized light of a fence-like pattern or
converting non-polarized light into non-polarized light of a lattice-like
pattern.
The projector of the present invention is such that the illuminating
optical system thereof has the polarizing conversion unit of the present
invention, or the image generator thereof has three generators for
generating red, green and blue images, respectively, and the illuminating
optical system has a color resolving system for resolving non-polarized
light into red, green and blue non-polarized lights, and the polarizing
conversion unit of the present invention provided in the optical path of
the non-polarized light of each color.
In the alternative image generator has three generators for generating red,
green and blue images, respectively, and the illuminating optical system
has a color resolving system for resolving non-polarized light into red,
green and blue non-polarized lights, and the polarizing conversion units
of the present invention provided in the common optical path of two of
non-polarized lights of three colors and the optical path of non-polarized
light of the other color, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the construction of the essential portions of a projector
according to the prior art.
FIG. 2 is a construction view of the unit 20 of a plate-like polarizing
element showing a first embodiment of the plate-like polarizing element of
the present invention.
FIG. 3 is a fragmentary view showing an example of the construction of a
plate-like polarizing element constructed by juxtaposing a plurality of
units 20 shown in FIG. 2.
FIG. 4 is a fragmentary view showing another example of the construction of
a plate-like polarizing element constructed by juxtaposing a plurality of
units 20 shown in FIG. 2.
FIG. 5 is a construction view of the unit 20a of a plate-like polarizing
element showing a second embodiment of the plate-like polarizing element
of the present invention.
FIG. 6 is a construction view of the unit 30 of a plate-like polarizing
element showing a third embodiment of the plate-like polarizing element of
the present invention.
FIG. 7 is a construction view of the unit 30a of a plate-like polarizing
element showing a fourth embodiment of the plate-like polarizing element
of the present invention.
FIG. 8 is a construction view of the unit 30b of a plate-like polarizing
element showing a fifth embodiment of the plate-like polarizing element of
the present invention.
FIG. 9 is a perspective view showing a portion of a first embodiment of the
polarizing conversion unit of the present invention.
FIG. 10 illustrates the operation of a both-surface lenticular lens 42
shown in FIG. 9.
FIG. 11 is a schematic construction view showing a first embodiment of the
projector of the present invention.
FIG. 12 is a schematic construction view showing a second embodiment of the
projector of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Some embodiments of the present invention will hereinafter be described
with reference to the drawings.
FIG. 2 is a construction view of the unit 20 of a plate-like polarizing
element showing a first embodiment of the plate-like polarizing element of
the present invention.
The unit 20 of the plate-like polarizing element of the present embodiment
comprises a first incidence side prism 21.sub.1 having the shape of a
triangle pole of right-angled triangular cross-section, first and second
emergence side prisms 22.sub.1 and 22.sub.2 having the same shape as the
first incidence side prism 21.sub.1 and disposed adjacent to the first
incidence side prism 21.sub.1 with their inclined surfaces in contact with
one another, a second incidence side prism 21.sub.2 having a half of the
shape of the first incidence side prism 21.sub.1 and disposed on that side
of the first emergence side prism 22.sub.1 opposite to the first incidence
side prism 21.sub.1 with their inclined surfaces in contact with each
other, and a third incidence side prism 21.sub.3 having the same shape of
the second incidence side prism 21.sub.2 and disposed on that side of the
second emergence side prism 22.sub.2 opposite to the first incidence side
prism 21.sub.1 with their inclined surfaces in contact with each other,
and the three incidence side prisms 21.sub.1 -21.sub.3 and the two
emergence side prisms 22.sub.1 and 22.sub.2 together constitute a plane
parallel plate. On the surface of contact between the first incidence side
prism 21.sub.1 and the first emergence side prism 22.sub.1, a first
quarter wavelength plate 23.sub.1 is provided on the first incidence side
prism 21.sub.1 side, and first polarization separation acting film
24.sub.1 is provided on the first emergence side prism 22.sub.1 side.
Further, on the surface of contact between the first incidence side prism
21.sub.1 and the second emergence side prism 22.sub.2, a second quarter
wavelength plate 23.sub.2 is provided on the first incidence side prism
21.sub.1 side, and second polarization separation acting film 24.sub.2 is
provided on the second emergence side prism 22.sub.2 side. A first total
reflection mirror 25.sub.1 is formed on the surface of contact between the
second incidence side prism 21.sub.2 and the first emergence side prism
22.sub.1, and a second total reflection mirror 25.sub.2 is formed on the
surface of contact between the third incidence side prism 21.sub.3 and the
second emergence side prism 22.sub.2. The first and second polarization
separation acting films 24.sub.1 and 24.sub.2 have the characteristic of
reflecting S-polarized light having a plane of polarization parallel to
the film surface and transmitting therethrough P-polarized light having a
plane of polarization perpendicular to the film surface. Also, the first
and second quarter wavelength plates 23.sub.1 and 23.sub.2 act on light
incident at an incidence angle of 45.degree. like first and second
incident lights P.sub.1 and P.sub.2, and the directions of the optical
axis thereof are selected so as to convert S-polarized light into
circularly polarized light.
That is, in the unit 20 of the plate-like polarizing element of the present
embodiment, the surface of contact between the first incidence side prism
21.sub.1 and the first emergence side prism 22.sub.1 and the surface of
contact between the first incidence side prism 21.sub.1 and the second
emergence side prism 22.sub.2 function as a pair of polarizing dividing
surfaces having substantially the same angles of inclination with respect
to non-polarized light (first and second incident lights P.sub.1 and
P.sub.2) and facing each other so that the reflected light from one of
them (first and second S-polarized lights L.sub.S1 and L.sub.S2) may
travel toward the others and the first and second polarization separation
acting films 24.sub.1 and 24.sub.2 function as a dividing portion which
divides the incident light into reflected light (first and second
S-polarized light L.sub.S1 and L.sub.S2) and transmitted light (first and
second P-polarized lights L.sub.P1 and L.sub.P2) whose planes of
polarization are orthogonal to each other. Also, the first and second
total reflection mirrors 25.sub.1 and 25.sub.2 function as a reflecting
portion which reflects one (first and second S-polarized lights L.sub.S1
and L.sub.S2) of the reflected light and the transmitted light) and
directs it substantially in the same direction as the direction of travel
of the other (first and second P-polarized lights L.sub.P1 and L.sub.P2).
Further, the first and second quarter wavelength plates 23.sub.1 and
23.sub.2 function as a modulating portion which varies the plane of
polarization of at least one (first and second S-polarized lights L.sub.S1
and L.sub.S2) of the reflected light and the transmitted light to thereby
make the planes of polarization of the two lights coincident with each
other.
The operation of the unit 20 of the plate-like polarizing element of the
present embodiment will now be described.
The first incident light P.sub.1 having a random plane of polarization
which is incident at an incidence angle of 45.degree. with respect to the
surface of contact between the first incidence side prism 21.sub.1 and the
first emergence side prism 22.sub.1 is divided into first P-polarized
light L.sub.P1 and first S-polarized light L.sub.S1 by the first
P-polarized light L.sub.P1 which is transmitted through the first quarter
wavelength plate 23.sub.1 and thereafter enters the first polarization
separation acting film 24.sub.1 and has a plane of polarization
perpendicular to the film surface being transmitted through the first
polarization separation acting film 24.sub.1 and the first S-polarized
light L.sub.S1 which has a plane of polarization parallel to the film
surface being reflected rightwardly at a right angle by the first
polarization separation acting film 24.sub.1. The first P-polarized light
L.sub.P1 emerges from the exit surface of the first emergence side prism
22.sub.1. On the other hand, the first S-polarized light L.sub.S1 is
transmitted through the first quarter wavelength plate 23.sub.1 and is
thereby converted into circularly polarized light, whereafter it is
transmitted through the second quarter wavelength plate 23.sub.2 and is
thereby converted into first converted P-polarized light L.sub.P1 * having
a plane of polarization perpendicular to the film surface of the second
polarization separation acting film 24.sub.2. The first converted
P-polarized light L.sub.P1 * is transmitted through the second
polarization separation acting film 24.sub.2, whereafter it is reflected
upwardly at a right angle by the second total reflection mirror 25.sub.2
and emerges from the exit surface of the second emergence side prism
22.sub.2 in the same direction as the direction of travel of the first
P-polarized light L.sub.P1.
Also, the second incident light P.sub.2 having a random plane of
polarization which is incident at an incidence angle of 45.degree. with
respect to the surface of contact between the first incidence side prism
21.sub.1 and the second emergence side prism 22.sub.2 is divided into
second P-polarized light L.sub.P2 and second S-polarized light L.sub.S2 by
the second P-polarized light L.sub.P2 which is transmitted through the
second quarter wavelength plate 23.sub.2 and thereafter enters the second
polarization separation acting film 24.sub.2 and has a plane of
polarization perpendicular to the film surface being transmitted through
the second polarization separation acting film 24.sub.2 and the second
S-polarized light L.sub.S2 which has a plane of polarization parallel to
the film surface being reflected leftwardly at a right angle by the second
polarization separation acting film 24.sub.2. The second P-polarized light
L.sub.P2 emerges from the exit surface of the second emergence side prism
22.sub.2. On the other hand, the second S-polarized light L.sub.S2 is
transmitted through the second quarter wavelength plate 23.sub.2 and is
thereby converted into circularly polarized light, whereafter it is
transmitted through the first quarter wavelength plate 23.sub.1 and is
thereby converted into second converted P-polarized light L.sub.P2 *
having a plane of polarization perpendicular to the film surface of the
first polarization separation acting film 24.sub.1. The second converted
P-polarized light L.sub.P2 * is transmitted through the first polarization
separation acting film 24.sub.1, whereafter it is reflected upwardly at a
right angle by the first total reflection mirror 25.sub.1 and emerges from
the exit surface of the first emergence side prism 22.sub.1 in the same
direction as the direction of travel of the second P-polarized light
L.sub.P2.
Accordingly, the unit 20 of the plate-like polarizing element of the
present embodiment can convert the first and second incident lights
P.sub.1 and P.sub.2 incident on the first incidence side prism 21.sub.1
into the first and second P-polarized lights L.sub.P1 and L.sub.P2 and the
first and second converted P-polarized lights L.sub.P1 * and L.sub.P2 *
without any loss and can cause them to emerge from the whole exit surface.
Description will now be made of the material of each constituent of the
unit 20 of the plate-like polarizing element of the present embodiment.
The first, second and third incidence side prisms 21.sub.1 -21.sub.3 and
the first and second emergence side prisms 22.sub.1 and 22.sub.2 can be
formed of glass or plastic, but to keep the separating function of the
first and second polarization separation acting films 24.sub.1 and
24.sub.2 optimal, those prisms may preferably be formed of glass having a
great degree of freedom of refractive index selection. Also, a combination
of plane parallel plates is possible instead of using prisms, but in such
case, the transmittance of P-polarized light is inferior to the case where
prisms are used. The first and second quarter wavelength plates 23.sub.1
and 23.sub.2 can be formed of a crystalline material such as mica or rock
crystal, dilated high molecular film, low molecular liquid crystal having
a predetermined thickness and oriented with the molecular axes thereof
uniformized in a predetermined direction, side chain type high molecular
liquid crystal or low molecular liquid crystal dispersed in high
molecules. The first and second polarization separation acting films
24.sub.1 and 24.sub.2 can be formed of conventional optical multilayer
film, but use can be made of any material having a polarization separation
characteristic such as cholesteric liquid crystal. As the first and second
total reflection mirrors 25.sub.1 and 25.sub.2, use may be made of
aluminum evaporated mirrors, or the second and third incidence side prisms
21.sub.2 and 21.sub.3 can be eliminated and those inclined surfaces of the
first and second emergence side prisms 22.sub.1 and 22.sub.2 which are
opposite to the first incidence side prism 21.sub.1 can be made into air
boundary surfaces to thereby form total reflection surfaces.
This unit 20 can be made thinner and lighter in weight than the combination
of the polarizing beam splitter 111 and the total reflection prism 112
shown in FIG. 1, and thus leads to the possibility of realizing a compact
and light-weight projector.
To construct a much thinner and lighter-weight polarizing element, the unit
20 can be made compact and a plurality of such units can be juxtaposed.
The polarizing element shown in FIG. 2, as compared with a polarizing
element as shown later in FIG. 5 wherein wavelength plate is disposed
parallel to the incident light, has the effect that no middle omission
occurs to the emergent light. This is because if the wavelength plate is
disposed parallel to the incident light, it is apparent that middle
omission will occur correspondingly to the thickness of the wavelength
plate.
An example of the construction in which a plurality of units 20 shown in
FIG. 2 are juxtaposed to construct a plate-like polarizing element is a
plate-like polarizing element 41 as shown in FIG. 3 wherein a plurality of
units 20 are laterally juxtaposed. Another example of the construction is
a plate-like polarizing element 41a as shown in FIG. 4 wherein adjacent
ones of rows each comprising a plurality of units 20 laterally juxtaposed
are arranged with the pitch thereof shifted by one half. In the plate-like
polarizing elements 41 and 41a shown in FIGS. 3 and 4, respectively, the
incidence side prisms which provide the connecting surfaces of adjacent
units (the second incidence side prism 21.sub.2 and the third incidence
side prism 21.sub.3 shown in FIG. 1) may be constructed integrally with
each other.
FIG. 5 is a construction view of the unit 20a of a plate-like polarizing
element showing a second embodiment of the plate-like polarizing element
of the present invention.
The difference of the unit 20a of the plate-like polarizing element of the
present embodiment from the unit 20 of the plate-like polarizing element
shown in FIG. 2 is that instead of the first and second quarter wavelength
plates 23.sub.1 and 23.sub.2, a half wavelength plate 26 is provided
intermediately of the surface of contact between the first incidence side
prism 21.sub.1 and the first emergence side prism 22.sub.1 and the surface
of contact between the first incidence side prism 21.sub.1 and the second
emergence side prism 22.sub.2.
In the unit 20a of the plate-like polarizing element of the present
embodiment, the first incident light P.sub.1 is divided into first
P-polarized light L.sub.P1 and first S-polarized light L.sub.S1 by the
first P-polarized light L.sub.P1 being transmitted through the first
polarization separation acting film 24.sub.1 and the first S-polarized
light being reflected rightwardly at a right angle by the first
polarization separation acting film 24.sub.1. The first P-polarized light
L.sub.P1 emerges from the exit surface of the first emergence side prism
22.sub.1. On the other hand, the first S-polarized light L.sub.S1 has its
plane of polarization rotated by 90.degree. by being transmitted through
the half wavelength plate 26 and is converted into first converted
P-polarized light L.sub.P1 *. The first converted P-polarized light
L.sub.P1 * is transmitted through the second polarization separation
acting film 24.sub.2, whereafter it is reflected upwardly at a right angle
by the second total reflection mirror 25.sub.2 and emerges from the exit
surface of the second emergence side prism 22.sub.2 in the same direction
as the direction of travel of the first P-polarized light L.sub.P1. The
second incident light P.sub.2 is divided into second P-polarized light
L.sub.P2 and second S-polarized light L.sub.S2 by the second P-polarized
light L.sub.P2 being transmitted through the second polarization
separation acting film 24.sub.2 and the second S-polarized light L.sub.S2
being reflected leftwardly at a right angle by the second polarization
separation acting film 24.sub.2. The second P-polarized light L.sub.P2
emerges from the exit surface of the second emergence side prism 22.sub.2.
On the other hand, the second S-polarized light L.sub.S2 has its plane of
polarization rotated by 90.degree. by being transmitted through the half
wavelength plate 26 and is converted into second converted P-polarized
light L.sub.P2 *. The second converted P-polarized light L.sub.P2 * is
transmitted through the first polarization separation acting film
24.sub.1, whereafter it is reflected upwardly at a right angle by the
first total reflection mirror 25.sub.1 and emerges from the exit surface
of the first emergence side prism 22.sub.1 in the same direction as the
direction of travel of the second P-polarized light L.sub.P2. Accordingly,
the unit 20a of the plate-like polarizing element of the present
embodiment also can convert the first and second incident lights. P.sub.1
and P.sub.2 incident on the first incidence side prism 21.sub.1 into the
first and second P-polarized lights L.sub.P1 and L.sub.P2 and the first
and second converted P-polarized lights L.sub.P1 * and L.sub.P2 * without
any loss and cause them to emerge from the whole exit surface. The half
wavelength plate 26 may be provided anywhere between the surface of
contact between the first incidence side prism 21.sub.1 and the first
emergence side prism 22.sub.1 and the surface of contact between the first
incidence side prism 21.sub.1 and the second emergence side prism
22.sub.2.
FIG. 6 is a construction view of the unit 30 of a plate-like polarizing
element showing a third embodiment of the plate-like polarizing element of
the present invention.
The unit 30 of the plate-like polarizing element of the present embodiment
is of a construction in which a dividing portion (polarization separation
acting film 34) is disposed obliquely with respect to non-polarized light
(incident light P), a reflecting portion (total reflection film 35) is
disposed parallel to the dividing portion and as a modulating portion, a
half wavelength plate 36 is disposed in the optical path of reflected
light (S-polarized light L.sub.S), particularly the optical path of the
reflected light (S-polarized light L.sub.S) reflected by the reflecting
portion (total reflection film 35).
That is, the unit 30 of the plate-like polarizing element of the present
embodiment comprises a first glass member 31.sub.1 of parallelogrammatic
cross-sectional shape and second and third glass members 31.sub.2 and
31.sub.3 of right-angled triangular cross-sectional shape arranged
adjacent to the both sides of the first glass member 31.sub.1 with the
inclined surfaces thereof in contact with one another, and the three glass
members 31.sub.1 -31.sub.3 together constitute a plane parallel plate.
Total reflection film 35 is provided on the surface of contact between the
first glass member 31.sub.1 and the second glass member 31.sub.2, and
polarization separation acting film 34 is provided on the surface of
contact between the first glass member 31.sub.1 and the third glass member
31.sub.3. Further, a half wavelength plate 36 is provided on the exit
surface of the first glass member 31.sub.1 (that surface of the first
glass member which is opposite to the surface on which the incident light
P is incident). The polarization separation acting film 34 has a
characteristic of reflecting S-polarized light having a plane of
polarization parallel to the film surface and transmitting therethrough
P-polarized light having a plane of polarization perpendicular to the film
surface. Also, the half wavelength plate 36 acts on light incident at an
incidence angle of 90.degree.. Accordingly, in the unit 30 of the
plate-like polarizing element of the present embodiment, the polarization
separation acting film 34 functions as a dividing portion which divides
the incident light into reflected light (S-polarized light L.sub.S) and
transmitted light (P-polarized light L.sub.P) whose planes of polarization
are orthogonal to each other. Also, the total reflection film 35 functions
as a reflecting portion which reflects one (S-polarized light L.sub.S) of
the reflected light and the transmitted light and directs it substantially
in the same direction as the direction of travel of the other (P-polarized
light L.sub.P). Further, the half wavelength plate 36 functions as a
modulating portion which varies the plane of polarization of at least one
(S-polarized light L.sub.S) of the reflected light and the transmitted
light to thereby make the planes of polarization of the two lights
coincident with each other.
The operation of the unit 30 of the plate-like polarizing element of the
present embodiment will now be described.
The incident light P having a random plane of polarization which is
incident on the film surface of the polarization separation acting film 34
at an incidence angle of 45.degree. is divided into P-polarized light
L.sub.P and S-polarized light L.sub.S by the P-polarized light L.sub.P
which has a plane of polarization perpendicular to the film surface being
transmitted through the polarization separation acting film 34 and the
S-polarized light L.sub.S which has a plane of polarization parallel to
the film surface being reflected leftwardly at a right angle by the
polarization separation acting film 34. The P-polarized light L.sub.P
emerges from the exit surface of the third glass member 31.sub.3 (that
surface of the third glass member which is opposite to the surface on
which the incident light P is incident). On the other hand, the
S-polarized light L.sub.S is reflected upwardly at a right angle by the
total reflection film 35 and emerges from the exit surface of the second
glass member 31.sub.2 in the same direction as the direction of travel of
the P-polarized light L.sub.P, whereafter it is transmitted through the
half wavelength plate 36, whereby it has its plane of polarization rotated
by 90.degree. and is converted into P-polarized light L.sub.P *.
Accordingly, the unit 30 of the plate-like polarizing element of the
present embodiment can convert the incident light P incident on the first
glass member 31.sub.1 into the P-polarized light L.sub.P and the converted
P-polarized light L.sub.P * without any loss and cause them to emerge from
the whole exit surface. In the present embodiment, polarization separation
acting film can also be used in lieu of the total reflection film 35.
Examples of the construction in which a plurality of units 30 shown in FIG.
6 are juxtaposed to construct a plate-like polarizing element include the
examples shown in FIGS. 3 and 4 wherein the units 30 are juxtaposed like
the units 20 shown in FIG. 2. The unit 30 shown in FIG. 6 can be
constructed by juxtaposing a plurality of glass members of
parallelogrammatic cross-sectional shape when constructing a plate-like
polarizing element and therefore, has the effect that it is more excellent
in workability than the unit 20 shown in FIG. 2. The unit 30 shown in FIG.
6 can be constructed by juxtaposing a plurality of glass members of
parallelogrammatic cross-sectional shape when constructing a plate-like
polarizing element and therefore, has the effect that it is more excellent
in workability than the unit 20 shown in FIG. 2. That is, the unit 30 can
be easily made by alternately laminating glass plates having polarization
separation acting film 34 provided on one surface thereof and glass plates
having total reflection film 35 (for example, aluminum evaporated film)
provided on one surface thereof, severing them along a cross-section of
45.degree., optically polishing the severed surfaces, and thereafter
adhesively securing a half wavelength plate 36 thereto.
FIG. 7 is a construction view of the unit 30a of a plate-like polarizing
element showing a fourth embodiment of the plate-like polarizing element
of the present invention.
The difference of the unit 30a of the plate-like polarizing element of the
present embodiment from the unit 30 of the plate-like polarizing element
shown in FIG. 6 is that a half wavelength plate .36 is disposed between
polarization separation acting film 34 (a dividing portion) and total
reflection film 35 (a reflecting portion).
In the unit 30a of the plate-like polarizing element of the present
embodiment, the incident light P is divided into P-polarized light L.sub.P
and S-polarized light L.sub.S by the P-polarized light L.sub.P being
transmitted through the polarization separation acting film 34 and the
S-polarized light L.sub.S being reflected leftwardly at a right angle by
the polarization separation acting film 34. The P-polarized light L.sub.P
emerges from the exit surface of the third glass member 31.sub.3. On the
other hand, the S-polarized light L.sub.S has its plane of polarization
rotated by 90.degree. by being transmitted through the half wavelength
plate 36 and is converted into P-polarized light L.sub.P *, whereafter it
is reflected upwardly at a right angle by the total reflection film 35 and
emerges from the exit surface of the second glass member 31.sub.2 in the
same direction as the direction of travel of the P-polarized light
L.sub.P. Accordingly, the unit 30a of the plate-like polarizing element of
the present embodiment can convert the incident light P incident on the
first glass member 31.sub.1 into the P-polarized light L.sub.P and the
converted P-polarized light L.sub.P * without any loss and cause them to
emerge from the whole exit surface.
FIG. 8 is a construction view of the unit 30b of a plate-like polarizing
element showing a fifth embodiment of the plate-like polarizing element of
the present invention.
The difference of the unit 30b of the plate-like polarizing element of the
present embodiment from the unit 30 of the plate-like polarizing element
shown in FIG. 6 is that the half wavelength plate 36 is adhesively secured
to the exit surface of the third glass member 31.sub.3 which is the
optical path of transmitted light (P-polarized light L.sub.P).
In the unit 30b of the plate-like polarizing element of the present
embodiment, the incident light P is divided into P-polarized light L.sub.P
and S-polarized light L.sub.S by the P-polarized light L.sub.P being
transmitted through the polarization separation acting film 34 and the
S-polarized light L.sub.S being reflected leftwardly at a right angle by
the polarization separation acting film 34. The P-polarized light L.sub.P
emerges from the exit surface of the third glass member 31.sub.3,
whereafter it is transmitted through the half wavelength plate 36 and
thereby has its plane of polarization rotated by 90.degree. and is
converted into S-polarized light L.sub.S * and emerges. On the other hand,
the S-polarized light L.sub.S is reflected upwardly at a right angle by
the total reflection film 35 and emerges from the exit surface of the
second glass member 31.sub.2 in the same direction as the direction of
travel of the converted S-polarized light L.sub.S *. Accordingly, the unit
30b of the plate-like polarizing element of the present embodiment can
convert the incident light P incident on the first glass member 31.sub.1
into the S-polarized light L.sub.S and the converted S-polarized light
L.sub.S * without any loss and cause them to emerge from the whole exit
surface.
In the present embodiment, polarization separation acting film can be used
in lieu of the total reflection film 35.
Again in the embodiments of FIGS. 6, 7 and 8, a single unit can be used as
the polarizing element instead of a plurality of units being juxtaposed.
In such case, a member for absorbing or reflecting the light travelling
toward the second glass member 31.sub.2 can be disposed on the entrance
side of the second glass member 31.sub.2, or light condensing means for
directing the light travelling toward the second glass member 31.sub.2 to
the first glass member 31.sub.1 can be disposed. If this is done, the
polarizing element, i.e., the unit 30, can be made to have substantially
the same width as the width of the illuminating light beam, and there can
be realized a polarizing element of about half the size of the
conventional polarizing element shown in FIG. 1 in each of the direction
of the optical axis and a direction perpendicular to the optical axis.
FIG. 9 is a perspective view showing a portion of a first embodiment of the
polarizing conversion unit of the present invention.
The polarizing conversion unit 40 of the present embodiment comprises the
plate-like polarizing element 41 shown in FIG. 3, and a both-surface
lenticular lens 42 which is provided on the incidence side of the
plate-like polarizing element 41 and which is converting means for
converting non-polarized light into non-polarized light of a lattice-like
pattern. The plate-like polarizing element 41 is disposed so as to be
substantially orthogonal to the optical axis of non-polarized light of a
lattice-like pattern emerging from the both-surface lenticular lens 42,
and transmits the non-polarized light of a lattice-like pattern
therethrough and converts it into substantially dense polarized-light.
Also, as shown in FIG. 10, on the incidence side surface of the
both-surface lenticular lens 42 for incident lights P.sub.1 -P.sub.3
(non-polarized lights), convergence acting surfaces 43.sub.1 -43.sub.3
comprising positive power lenses having the function of converging the
incident lights P.sub.1 -P.sub.3 are provided at the same pitch as the
units 20.sub.1 -20.sub.3 of the plate-like polarizing element 41. Also, on
the emergence side surface of the both-surface lenticular lens 42 for the
incident lights P.sub.1 -P.sub.3, divergence acting surfaces 44.sub.1
-44.sub.3 comprising negative power lenses having the function of causing
the converged incident lights P.sub.1 -P.sub.3 to diverge and become
parallel lights are provided so as to be opposed to the first incidence
side prisms 21.sub.1 (see FIG. 2) of the units 20.sub.1 -20.sub.3.
Further, non-acting surfaces 45.sub.1 and 45.sub.2 which are flat surfaces
are provided between the divergence acting surfaces 44.sub.1 -44.sub.3.
Accordingly, incident lights P.sub.1 -P.sub.3 incident on the entrance
surface of the both-surface lenticular lens 42 perpendicularly thereto are
converged by the convergence acting surfaces 43.sub.1 -43.sub.3, whereby
as shown in FIG. 10, they do not enter the non-acting surfaces 45.sub.1
and 45.sub.2 but enter only the divergence acting surfaces 44.sub.1
-44.sub.3, whereafter they are made into parallel lights by the divergence
acting surfaces 44.sub.1 -44.sub.3 and emerge therefrom and therefore, the
light emerging from the both-surface lenticular lens 42 becomes
non-polarized light of a lattice-like pattern. This non-polarized light of
a lattice-like pattern is converted into polarized light by the plate-like
polarizing element 41, whereafter it emerges from the whole of the exit
surfaces of the units 20.sub.1 -20.sub.3. By making the absolute value of
the focal length of the divergence acting surfaces 44.sub.1 -44.sub.3 half
the focal length of the convergence acting surfaces 43.sub.1 -43.sub.3,
the beam width of the non-polarized light of a lattice-like pattern
emerging from the both-surface lenticular lens 42 can be made half the
pitch of the convergence acting surfaces 43.sub.1 -43.sub.3. Also, by
providing absorbent film on the non-acting surfaces 45.sub.1 and 45.sub.2,
the adverse effect by irregular reflection or the like can be mitigated.
The polarizing conversion unit 40 of the present embodiment has the
following advantages:
(1) Since the incident lights P.sub.1 -P.sub.3 are converted into
non-polarized lights of a lattice-like pattern by the both-surface
lenticular lens 42 and are caused to enter the units 20.sub.1 -20.sub.3 of
the plate-like polarizing element 41, the sizes of the units 20.sub.1
-20.sub.3 can be made small. Also, to make the sizes of the units 20.sub.1
-20.sub.3 of the plate-like polarizing element 4I further smaller, the
pitch of the convergence acting surfaces 43.sub.1 -43.sub.3 of the
both-surface lenticular lens 42 can be made small and the number of
divisions of the lattice-like pattern can be increased.
(2) Even if the light source is one having a finite diameter, the incident
lights P.sub.1 -P.sub.3 enter the first and second polarization separation
acting films 24.sub.1 and 24.sub.2 of the units 20.sub.1 -20.sub.3 of the
plate-like polarizing element 41 without fail and therefore, the
utilization efficiency of the light and the degree of polarization of the
emergent light can be improved. Particularly, the reflectance of the first
and second polarization separation acting films 24.sub.1 and 24.sub.2 for
S-polarized light can be relatively easily made 100% and therefore, the
degree of polarization of the emergent light can be kept high.
(3) The first, second and third incidence side prisms 21.sub.1 -21.sub.3
and the first and second emergence side prisms 22.sub.1 and 22.sub.2 which
are the constituents of the units 20.sub.1 -20.sub.3 of the plate-like
polarizing element 41 can be made identical in shape and size and
therefore, in the process of manufacture, the kinds of parts can be
decreased and low cost can be achieved. Particularly, the kinds of the
prisms which occupy a great rate in terms of cost can be decreased and
therefore, the effect of low cost is very great.
When the ease of molding and optical characteristics such as transmittance,
etc. are taken into account, the both-surface lenticular lens 42 may be
one provided by extrusion-molding or compression-molding an acryl plate.
However, where the heat resisting property is particularly required, it is
preferable to use one provided by compression-molding or polish-molding a
glass member. Also, the both-surface lenticular lens 42 may be constructed
by unitary molding, or may be constructed by cementing one-surface
lenticular lenses together. Also, where the light source has a finite
diameter, the ratio between the light beam presence area and the light
beam absence area of the non-polarized light of a lattice-like pattern can
be made 1:1 by making the absolute value of the focal length of the
divergence acting surfaces 44.sub.1 -44.sub.3 less than half the focal
length of the convergence acting surfaces 43.sub.1 -43.sub.3.
The polarizing conversion unit 40 of the present embodiment is constructed
by the use of the plate-like polarizing element 41 shown in FIG. 3 and the
both-surface lenticular lens 42, but alternatively, it may be constructed
by the use of a plate-like polarizing element comprising the units 20a,
30, 30a, 30b shown in FIGS. 5-8 and a both-surface lenticular lens.
A second embodiment of the polarizing conversion unit of the present
invention will now be described.
The polarizing conversion unit of the present embodiment comprises the
plate-like polarizing element 41a shown in FIG. 4, and a both-surface
fly-eye lens which is converting means for converting non-polarized light
into non-polarized light of a two-dimensional lattice-like pattern
provided on the entrance side of the plate-like polarizing element 41a. In
the polarizing conversion unit of the present embodiment, the incident
light is vertically and horizontally divided by the both-surface fly-eye
lens, whereafter it is caused to enter the first incidence side prism
21.sub.1 of each unit 20.sub.1 -20.sub.5 of the plate-like polarizing
element 41a. Again in the present embodiment, the polarizing conversion
unit may be constructed by the use of a plate-like polarizing element
comprising the units 20a, 30, 30a, 30b shown in FIGS. 5-8 and a
both-surface fly-eye lens.
FIG. 11 is a schematic construction view showing a first embodiment of the
projector of the present invention.
The projector of the present embodiment differs from the projector shown in
FIG. 1 in that it uses the polarizing conversion unit 40 shown in FIG. 9
as an illuminating optical system for converting the parallel white light
(non-polarized light) from a first condenser lens 64 into white
rectilinearly polarized light. In the projector of the present embodiment,
a second condenser lens 65 for condensing the white rectilinearly
polarized light from the polarizing conversion unit 40 into the pupil of a
projection lens 68 is provided between the polarizing conversion unit 40
and a liquid crystal light valve 66.
Accordingly, the projector of the present embodiment illuminates the liquid
crystal light valve 66 by the use of the polarizing conversion unit 40
which is the polarizing conversion unit of the present invention and
therefore, white light (non-polarized light) emitted from a light source
61 can be caused to enter the liquid crystal light valve 66 without any
loss and the distance from the light source 61 to the liquid crystal light
valve 66 can be made short and thus, the projector can be made compact.
FIG. 12 is a schematic construction view showing a second embodiment of the
projector of the present invention.
The projector of the present embodiment comprises a light source 71
emitting non-polarized light (white light), a reflecting mirror 72, a heat
cut filter 73, a first condenser lens 74, an illuminating optical system
for converting the non-polarized light from the light source into
polarized light, an image generating portion for generating an image by
modulating the polarized light in conformity with a video signal, and a
projecting optical system for projecting system is comprised of a color
resolving system comprising a first resolving dichroic mirror 81, a second
resolving dichroic mirror 82 and a resolving and reflecting mirror 83 for
resolving the white light which is non-polarized light into red, green and
blue non-polarized lights, respectively, polarizing conversion units
40.sub.R, 40.sub.G and 40.sub.B provided in the optical paths of the
respective non-polarized lights and similar in construction to the
polarizing conversion unit 40 shown in FIG. 9, a condenser lens 75.sub.R
for red, a condenser lens 75.sub.G for green and a condenser lens 75.sub.B
for blue. The image generating portion comprises a liquid crystal light
valve 76.sub.R for red, a liquid crystal light valve 76.sub.G for green
and a liquid crystal light valve 76.sub.B for blue which are three
generators for generating red, green and blue images, respectively.
Further, the projecting optical system comprises a first combining
dichroic mirror 84, a combining and reflecting mirror 85, a second
combining dichroic mirror 86 and a projection lens 78.
In the projector of the present embodiment, red non-polarized light P.sub.R
is reflected upwardly at a right angle by the first resolving dichroic
mirror 81, blue non-polarized light P.sub.B of cyan non-polarized light
P.sub.G +P.sub.B transmitted through the first resolving dichroic mirror
81 is transmitted through the second resolving dichroic mirror 82 and
green non-polarized light P.sub.G is reflected upwardly at a light angle
by the second resolving dichroic mirror 82, whereby parallel white light
P.sub.R +P.sub.G +P.sub.B emerging from the first condenser lens 74 which
is non-polarized light is resolved into red, green and blue non-polarized
lights P.sub.R, P.sub.G and P.sub.B. The red non-polarized light P.sub.R
is reflected leftwardly at a right angle by the resolving and reflecting
mirror 83, whereafter it enters the polarizing conversion unit 40.sub.R
for red and is converted thereby into red polarized light. The green
non-polarized light P.sub.G is reflected by the second resolving dichroic
mirror 82, whereafter it enters the polarizing conversion unit 40.sub.G
for green and is converted thereby into green polarized light. Further,
the blue non-polarized light P.sub.B is transmitted through the second
resolving dichroic mirror 82, whereafter it enters the polarizing
conversion unit 40.sub.B for blue and is converted thereby into blue
polarized light.
The red polarized light enters the liquid crystal light valve 76.sub.R for
red through the condenser lens 75.sub.R for red, and has its plane of
polarization rotated in conformity with the red component of a color video
signal, whereby it is modulated and becomes a light beam including both of
P-polarized light and S-polarized light, and is further converted into
rectilinearly polarized red image light R* by a polarizing plate 77.sub.R
for red. Likewise, the green polarized light is converted into green image
light G* modulated by the action of the liquid crystal light valve
76.sub.G for green and a polarizing plate 77.sub.G for green in conformity
with the green component of the color video signal, and the blue polarized
light is converted into blue image light B* modulated by the action of the
liquid crystal light valve 76.sub.B for blue and a polarizing plate
77.sub.B for blue in conformity with the blue component of the color video
signal.
The red image light R* and the green image light G* are combined by the
first combining dichroic mirror 84 and converted into yellow image light
R*+G*, whereafter it enters the second combining dichroic mirror 86. The
blue image light B* is reflected upwardly at a right angle by the
combining and reflecting mirror 85, whereafter it enters the second
combining dichroic mirror 86. The yellow image light R*+G* is transmitted
through the second combining dichroic mirror 86 and the blue image light
B* is reflected leftwardly at a right angle by the second combining
dichroic mirror 86, whereby the yellow image light R*+G* and the blue
image light B* are combined and converted into white image light R*+G*+B*
modulated in conformity with the color video signal. The white image light
R*+G*+B* is enlarged and projected onto a screen (not shown) by the
projection lens 78 and thus, a color image is displayed on the screen.
The projector of the present embodiment has a polarizing conversion unit
for each of red, green and blue non-polarized lights P.sub.R, P.sub.G and
P.sub.B and thus, has the following effects:
(1) Since it is difficult to make the wavelength dependency of the quarter
wavelength plate and polarization separation acting film (see FIG. 2) used
in each of the polarizing conversion unit 40.sub.R for red, the polarizing
conversion unit 40G for green and the polarizing conversion unit 40.sub.B
for blue zero, it can more improve to use red, green and blue
non-polarized lights P.sub.R, P.sub.G and P.sub.B as the incident light
than to use wide-band non-polarized light like parallel white light
P.sub.R +P.sub.G +P.sub.B as the incident light.
(2) Generally, the light source 71 has a finite diameter and therefore,
white light emitted from the light source 71 always has a finite angle of
expanse. If the beam diameter of light having a finite angle of expanse is
compressed by some optical system, the angle of expanse will become
greater in inverse proportion to the compression ratio of the beam
diameter. Accordingly, in the prior-art projector shown in FIG. 1, the
light condensing efficiency onto the liquid crystal light valve 117 will
be reduced by an increase in the angle of expanse of light even if the
beam diameter of light having a finite angle of expanse is compressed,
because the distance between the polarizing conversion unit and the liquid
crystal light valve 117 is great. On the other hand, in the projector of
the present embodiment, thin planar polarizing conversion units are used
and therefore, these polarizing conversion units can be installed in
proximity to the liquid crystal light valves and thus, the reduction in
the light condensing efficiency onto the liquid crystal light valve 117 by
an increase in the angles of expanse of the red, green and blue
non-polarized lights P.sub.R, P.sub.G and P.sub.B.
A third embodiment of the projector of the present invention will now be
described.
The projector of the present embodiment differs from the projector shown in
FIG. 12 in that it has a polarizing conversion unit for cyan provided
between the first resolving dichroic mirror 81 and the second resolving
dichroic mirror 82 (i.e., in the common optical path of the green
non-polarized light P.sub.G and the blue non-polarized light P.sub.B), in
lieu of the polarizing conversion unit 40.sub.G for green and the
polarizing conversion unit 40.sub.B for blue.
Where a plurality of polarizing conversion units are used, it is better
from the viewpoints of the utilization efficiency of the light emitted
from the light source and the suppression of the occurrence of color
irregularity to dispose the polarizing conversion units at optically
equivalent positions (positions equivalent in the direction of travel
amplitude, etc. of the light) and therefore, it is desirable to construct
the projector like that shown in FIG. 12, but where preference is given to
the curtailment of the number of parts, even if the projector is
constructed like that of the present embodiment to thereby decrease the
number of polarizing conversion units, the utilization efficiency of light
can be more improved than in the prior-art projector and the entire
apparatus can be made compact.
In the projector shown in FIG. 12, as the polarizing conversion units
40.sub.R, 40.sub.G and 40.sub.B for respective colors, use may be made of
ones each comprising a combination of a plate-like polarizing element
consisting of the unit 20a, 30, 30a, 30b shown in FIGS. 5-8 and a
both-surface lenticular lens, or ones each comprising a combination of the
plate-like polarizing element 41a shown in FIG. 4 and a both-surface
fly-eye lens. The construction of the projector of the present invention
is not restricted to the construction shown in FIG. 12, but in a projector
as described in Japanese Laid-Open Patent Application No. 62-59919 wherein
white light is resolved into respective color lights by the use of
respective color filters and the respective color lights modulated by a
liquid crystal light bulb are combined by a cube prism, the polarizing
conversion unit 40 shown in FIG. 9 may be disposed for each of the color
filters. Also, in a projector as described in Japanese Laid-Open Patent
Application No. 62-1391 wherein white light is resolved into respective
color lights by a first cube prism and the color lights modulated by a
reflection type liquid crystal light bulb are combined by a second cube
prism, the polarizing conversion unit 40 shown in FIG. 9 may be disposed
on the exit surface of the first cube prism for each color light.
As described above, the present invention has the following effects.
The polarizing element of the present invention can be made small in the
size thereof for the direction of travel of the incident light and a
direction perpendicular to the direction of travel of the incident light.
Also, the polarizing element of the present invention can be made compact
and by juxtaposing a plurality of such elements, the size thereof for the
direction of travel of the incident light can be made much smaller. The
polarizing conversion unit of the present invention can cause the incident
light to enter, without any loss, the plate-like polarizing element of the
present invention having between units an area in which the incident light
is intercepted when a plurality of polarizing elements are juxtaposed, and
can convert the incident light into polarized light without any loss by
the plate-like polarizing element and cause it to emerge therefrom and
therefore, can improve the utilization efficiency of light. Further, the
projector of the present invention can convert non-polarized light emitted
from the light source into polarized light without any loss by the
polarizing conversion unit and can therefore improve the utilization
efficiency of light and can make the distance between the polarizing
conversion unit and the image generator small, and this leads to the
compactness of the entire apparatus.
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